The organization of rodent visual cortex is particularly relevant because rodents are the predominant model for most laboratory studies, including behavioral studies, whole animal physiology, slice physiology, anatomical and molecular studies, and anatomical and genetic manipulations. Despite the fact that rodents are the most widely used model to study the brain, including the neocortex, there are still large issues regarding cortical organization that remain unresolved. In terms of the visual system, there is a debate regarding the organization of the extrastriate visual cortex of rodents in which as few as one visual field and as many as five visual fields have been proposed to border V1 or striate cortex laterally in mice and rats. This uncertainty is a good example of the difficulties in parcellation of the neocortex into distinct areas and the functional significance of multiple representations in the neocortex. The long-term objective of this study is to better understand the basic mammalian plan of visual cortex organization, and the way in which this plan has been modified to generate visually mediated behaviors associated with the demands of different niches. In order to accomplish this we will determine the differences in the organization of the visual cortex that are associated with a diurnal versus a nocturnal lifestyle in rodents using wild-caught California ground squirrels (Spermophilus beecheyi) and wild-caught rat (Rattus norvegicus). Individuals of these two species have overlapping ranges in California but very different visual lifestyles and structural/visual morphology. Use of wild-caught rodents is important in these comparisons as differences in a diurnal versus nocturnal lifestyle have not been teased apart from differences in rearing conditions in previous comparisons between diurnal and nocturnal rodents. To achieve the goals of this proposal we will combine electrophysiological recordings, histological techniques, and neuroantomical data to make direct comparisons between the size, functional organization, connections of V1, and the organization and number of cortical fields that adjoin the v1 boundary in architectonic area 18/18a. PUBLIC HEALTH RELEVANCE The strength of this proposal lies in the use of a combination of techniques and the use of wild-caught rodents to identify and characterize the visual cortex of diurnal and nocturnal rodents. The results from these studies will provide insight into the evolution of the visual cortex in rodents, and will be applicable to all studies of diurnal and nocturnal mammals.